1. Field of the Invention
The present invention relates to a sense amp circuit and a semiconductor memory device using the same. In more detail, it relates to a sense amp circuit suitably applicable in a semiconductor memory device that uses an antifuse element of the gate insulator destruction type in a memory cell, and to a semiconductor memory device.
2. Description of the Related Art
In a recent large capacity semiconductor memory device, a relatively small capacity, nonvolatile memory device is mounted in combination on the same chip to store an address of a failed memory element contained. Similarly, also in a high-function, high-speed semiconductor logic circuit device, a relatively small capacity, nonvolatile memory element is mounted in combination for the purpose of holding production information and of storing an individual chip intrinsic number. Similarly, also in a high-precision analog circuit device, a relatively small capacity, semiconductor memory device is mounted in combination as well to store adjustment information for keeping the characteristic uniform.
As the semiconductor memory device employed in the above use, a semiconductor memory element called antifuse element operative to store 1-bit data by destroying a gate insulator of a MOS transistor is used, as found in examples. (See, for example, H. Ito et al., “Pure CMOS One-time Programmable Memory using Gate-OX Antifuse”, Proceedings of the IEEE 2004 Custom Integrated Circuits Conference, PP. 469-472.) The antifuse element of the gate insulator destruction type is characterized in that it can be produced inexpensive without the need for any additional production step to the production thereof. Furthermore, since it is characterized in that it does not need any additional production step, it does not suffer from any deterioration of properties of major semiconductor elements mounted in combination on the same chip, such as fine-patterned memory elements for large capacity storage, high-speed transistors contained in high-speed logic circuits, and transistors for analog circuits exhibiting a high-precision electrical property. With these excellent characteristics, the antifuse element may be referred to as an optimal nonvolatile memory element for the above use.
A nonreversible memory element, such as the antifuse element, capable of holding data by destroying the internal structure or the composition of the constitutional substances may often be not excellent in reading electrical property. For example, the change in the amount of read current in accordance with the change in state is small, or the associated variation is large, or application of an appropriate voltage is required to obtain as large read current as some extent. Configuring a semiconductor memory device with such the memory element not excellent in reading electrical property can not lack the use of a high-precision sense amp that applies an appropriate bias voltage, accurately amplifies a very small read-out potential difference, and decides “0”/“1” of output data at appropriate timing.
Conventionally used high-precision sense amps operative to amplify a very small differential potential difference include a differential amplifier of the analog operation type. In general, an analog differential amplifier has advantages because a higher amplification rate can be set and a high-precision sense amp can be designed easily. To the contrary, the differential amplifier of the analog operation type has disadvantages because it consumes larger power and has a larger layout area.
On the other hand, the sense amp including the latch circuit has advantages because it has a simpler configuration and a smaller layout area, operates under a lower voltage, and consumes smaller power since current flows only at the instant of sensing. To the contrary, it has disadvantages because it has a lower amplification rate and a lower precision in comparison with the sense amp including the analog differential amplifier.